Ramo transmission system



May 27, 1947. H. W.' K'LxNE RADIO T'amsmsslou sYsTEM Original Filed Feb. 21. l1941 HE CARR/ER RECE/I/ER HHS Attorney.

May 27, 1947.'v

H. W. KLINE RADIO vTRANSMISSION SYSTEM Original Filed Feb. 2l, 1941 2 Sheets-Shee't 2 ,5 '460. SENER/'70N d, Inventor:

HaISeyWKh, bymf/ Reissued May 27, 1947 RADIO TRANSMISSION SYSTEM Halsey W. Kline, Schenectady, Y., assignor to General Electric Company, a corporation of New York yOriginal No. 2,334,011, dated November 9, 1943,

Serial No. 380,021, February 21, 1941. Application for reissue January 29, 1947, Serial No.

14 Claims.

This invention relates to a signal transmission system, and more particularly to a carrier wave system for transmitting signals in which fading is minimized or eliminated.

In the art of radiol communication it is well known that a radio wave of medium or high frequency often cannot be received within a zone which may, for example, lie (for a 20 meter wave) between 50 and 700 miles from the transmitter. In other words, under a certain set of conditions, the wave may, for example, be received only within 50 miles of the transmitter, or farther than 700 miles from it. The width of such a zone in which the transmitted wave cannot be received is commonly termed the skip distance. It is usually assumed that this skip exists because a radio wave from a transmitter moves near the ground only for a short distance before it becomes attenuated to an intensity too low to be received, while ionized layers in the upper atmosphere reiiect the wave from the transmitter to positions much farther removed than those to which the ground Wave reaches. Varying reflection from the ionized layers produces fading.

It is an object of my invention to provide an improved signal transmission system by which communication may be carried on at distances from the transmitter within the normal skip distance.

` It is also an object of my invention to provide an improved signal transmission system in which fading effects are minimized.

To attain these objects I utilize a system in which a radio wave, for example, is radiated in such a way that a directional characteristic malr be changed. If the radiation is in the form of a beam, the direction of propagation of the beam may be altered periodically. As the beam direction is periodically altered, reflection from the ionized layers varies in direction and position, so that many points not reached by a wave propagated in a single direction are reached intermittently by such radiation whose direction of propagation is altered. Alternatively, a polarized wave may be radiated and the direction of polarization altered intermittently to produce similar results.

When either of these directional characteristics is altered, the intensity of radiation is preferably kept constant, whereby fading is reduced at distant points to which such radiation is reflected from upper strata of the atmosphere. In particular, selective fading, due to unequal transmission of side bands, is lessened.

It is accordingly a particular object of my invention to provide an improved signal transmission system for transmitting a signal over a carrier wave whose amplitude and frequency are maintained constant at all times.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantagesthereof may best be understood by reference to the following description taken in connection with the accompanying drawings in which Fig. l illustrates a radio transmitter constructed according to my invention in which the direction of propagation of a radio beam is altered; Fig. 2 illustrates certain characteristics of my signal transmission system; Fig. 3 illustrates a receiver for receiving waves from the transmitter illustrated in 1; and Fig 4 illustrates a form of my invention in which the polarization of a wave is altered.

In Fig. 1 the transmitter includes a tuned circuit I0, which is maintained in oscillation by an electron discharge device II, and from which oscillations are amplified in a high frequency carrier transmitter I2 and radiated from a dipole antenna I3. One terminal of the tuned circuit I is grounded and is coupled to the anode I4 of the device I I through a coupling condenser I5. The other terminal of the tuned circuit I0 is connected through a conductor I6 to the transrmitter I2 and is coupled through a condenser I'I, shunted by a resistance I8, to the control electrode I9 of the device II. The cathode 20 of the device II is connected to an intermediate point of the tuned circuit I 0. The anode I4 is connected through a resistance 2l and source 22 of operating potential. The tuned circuit I0 and accompanying elements thus form a usual type of oscillator.

The dipole antenna I3 lies parallel to the surface of the earth and at a distance above the surface of the earth equal to one-quarter wave length of the Wave impressed on the antenna. A similar dipole antenna 23 is placed parallel to the antenna I3 and lies one-quarter wave length from the antenna I3 and one-quarter wave length above the surface of the earth. The dipole antenna 23 is interrupted at its center, and the interruption is bridged' by a series resonant circuit comprising an inductance 24, a condenser 25, and an electron discharge device 26.

The dipole antenna 23 is arranged to act as a reflector of the waves radiated from the antenna I3. This reflecting antenna 23, by adjustment of the resonant frequency of the series resonant circuit comprising the inductance 24, the condenser 25, and the discharge device 26, may be made more or lesseiective to reiiect radiated Waves of aparticular frequency. `When thefr'esbnant frequency of the series resonant circuit is made equal to the frequency of waves radiated from the antenna I3, the antenna 23 is, in effect, connected together at its center -so :as to act most effectively as a reector Yforwavesfrom the antenna I3. When so adjusted thefantrina system acts to radiate waves in a direction substantially opposite to the direction of the antenna 23 from the antenna I3. Y

When the resonant freqixe'ricyif the-'series Isonant circuit is adjusted to 'a frequency different from that of the waves radiated fromwthe `antenna I3, the reflectingantenna 23 is effectively interruptedat its center,1 and does not reidectA waves f` si'ch frequency. `Wlrens`o' adjusted, fthe Atritt-inrias' stem radiateswavesupward f'romthe lantenna 3, becauseof :the r`1"eiire'ct'irrg power of the 'surface f th'e earth. Therefore, byadj'tstment of the resonant frelli'n'cycitheserie'sres nant eirculteomp'rlsi'ng tne mdujctance r24,111@ fcndenserf, and "the dischargedevi'ce A26, the direction, 'in a 'vertical plane, in which waves from the 'antenna "13 `are "radiated, may :be ad- `Jsted. v n Y' 'The electron "discharge "device 26, which is a v part'of theseriesrso'rant circuitfisj so connect- 'ldihshnt tdtheacb'ndenser as "to transmit uther'aro'und "a current 'Whose pha'se leads "the "phase of vtm-age "across-condenser 25 by a substantial "a'ngle "and, which 'therefore' `lsinfiu'latle's a "cnd''sr' c'rited in' shunt tnc'ohd'enser 25. Theanc'deZl of'the dvce"2;6 `is"connected to'a Y point b'etwehthe inductanc'e '24 an'd "dn'e'termigain trthe eenden-ser 25, andtneeatnode a3-is 40 nd "a" pont'between* the *choke-con 3`na1idthe resistance 3l. "Ivhesiir'ce 46"ma'int'ainsa'sliit- *ablefbias' potential-fr the contraitier-,tradesa,v Alternating potential fbetween the janode 21 ^`and the' "cathode "33 is impressed 'across these'r'ies (combination .of cnde'n'ser "'31 `andreslst'a'l'ice J3i), whereby alternating current 'of VVAleading jphase Y:nfld/Ws Athrough the condenser 'fand resistance. Y 'Colis'etmeritiy,A analteinatlng" voitgeiof leading Ero "-26 inilts yactidnlin simulating a condenser.

phase, with respect to the voltage between the anode 21 and cathode 33, is developed across the resistance 39, and applied to the control electrode 38. Alternating current which flows through the device16 is in phase with-theleading .alternating potntial'n j-thecontrol electrodes :38. Any a1- ternating potential which exists between the anfode 21 and the cathode 33 of the device 26 is, therefore, accompanied by a leading alternating currextfso that the device 26 simulates a condenser.

`Th`efanfointdfleading current Which flows throughthedevicefZG may be adjusted by changing the potential across the resistance 39, there- 'ibych'angingthe apparent reactance of the device As '"the'apparentractance of the device 2B changes, the -resonant frequency of the series resonant 'circuit including inductance 24, condenser 25, and discharge device 26, changes with a concur- 'rerit change in the direction of i'maximum"radia- 'ftion 'from 'th'e antenna ifa.

y'Audio v'signals fromaimicrphneuareamplifled in amplifier 43 andiappliediacross the-resistance39 `Vso as to change'thedirection df maxi- 'mum radiation from "the antenna gI 3 in accordance With fthe intensity of the laudio :signal-s Ito ybe transmitted. The J'nutpdt circit 'ff iamplifier "413 Iincludes V#a Switch *491 having three psiti'ns and jwhich, in gthe `f position shown, supplies 'the ampliedsiglrais "across resistlnce throughresistaneei-St. 1Its= operation iwhen 1in the futher-of its -Ipes'iticirrs -Wil1 --lalter befindicated.

v The 'transmitter as" thusdescribednraybead- `justedfin -several Ways. The source offpotcn- -tial may 'he made Ijust largefeno'ugh to makeithe *apparent -reactancedf the'device 2`6, in ithe Mairsence` of; a "signal A4fromi the microphone l2 ofthe jp'ro'per value to 'make theserie's' resonant `circuit, includ'rig Lin'ducta'rnse 524; condenser 25, an"d"1dis charge device 26, iresonate at the Cfrequency Iof `-Waves wfroinjthe antenna I"'I3. The output'offthe audio amplifier W3 *mayL-thenl'be pole'din either *directionsof-thatE the apparent freacta'nce'f the device 26 either increases or decreases'astheiintensity'o'f the--audioisignal increases. v'hange of reactance'iny 'eitherf'directioni changesi 'the-I resonant 4frequency f the "seiies resonant clrc'it,

land reduces the 'ffectivenessff-the antenna asV a reector, so that the direction offraidiaticn tensity ef ftheazieio '-signl.

Alternatively the potential i from the` sourced 4 D resonant circuit resonant' -atsaifrequeney'removed byaniano'unt equa1to-'the shiftof resonant frequency causedE hy* tha-average peak; 'intensity `Vnf v*are constant at^a1l't-irnes,Y thefmethcd off-transmission f' which'fcornprise's lvarying the :direction aant-receiver' 'orreeelvermoreforress um ated Wave therefore appearstobeimdulatdriwmnplitude, although it is in fact modulated in direction of propagation.

Referring to Fig. 2, there may be obtained a clearer idea. of the manner in which the radiation received at the distant receiver varies as the direction of propagation is changed at the transmitter. The transmitter is represented by an antenna 68 at a certain position on the surface of the earth 62. An ionic reflection layer is repsented by a dotted line 6| parallel to the surface of the earth 62. A distant receiver is represented by a second antenna 63. In the figure three different lines 64, 65, and 66 represent three different paths over which the radiation from the transmitter 68 travels at three different instants of time. The path 64 is nearly horizontal at the transmitter 68, indicating that the antenna 23 is effective as a reflector. The paths 65 and 66 are progressively nearer vertical, indicating that the antenna 23 is correspondingly less effective as a reflector.

The wave which takes the path 64 travels a long distance before being reflected from the ionic layer 6| to travel a return path 61, which reaches the earth at a point far beyond the receiver 63. The wave which travels the second path 65 reaches the ionic layer 6| at a shorter distance, and is reflected at a more acute angle along a path 68, which passes close to the receiver 63 to be reflected again from the surface of the earth 62 along a path 69. The wave which travels the third path 66 is reflected from the ionic layer 6| at a point even closer to the transmitter 68, and takes the path 18 so as to be reflected from the earth 62 at a point between the transmitter 68 and the receiver 63. After reflection from the earth, this wave takes a path 1| back to the ionic layer 6|, and is again reflected therefrom along a path 12 to a pointon the surface of the earth 62 beyond the receiver 63.

By consecutive inspection of these three paths of radiation travel, it may be seen that energy from the transmitter 68 reaches the receiver 63 at least once during each time the path of travel of the beam from the transmitter 68 is varied in a vertical plane, In order to avoid distortion of the signal at the receiver 63, it is desirable to adjust the angle through which the carrier wave beam is swept in the vertical plane, so that the beam passes the receiver substantially only once during each sweep. Of course, it is Within the scope of the invention to sweepthe beam in a horizontal, or an other, plane and similar precaution should be taken to avoid distortion.

The transmitter illustrated in Fig. 1 may be caused to operate in a diierent way. The beam radiated from the antenna I3 may be caused to sweep up and down in a vertical plane at a predetermined frequency when there is no signal from the microphone, and to sweep up and down in a vertical plane at differing frequencies for various intensities of signal from the microphone 42. To reconnect the transmitter to accomplish this, the blades of the switch 41 are moved downward to connect the output of the audio ampifier 43 through an electron discharge device 88, which controls the operating frequency of an oscillating electron discharge device 8|, which in turn is connected to supply alternating potential across the resistance 39.

The discharge device 8| is connected with 'a tuned circuit, comprising an inductance 82 and a condenser 83, to form an oscillator and maintain continuous oscillations. The cathode 84 of the device 8| is connected to an intermediate point of the inductance 82, of which one terminal is grounded. This grounded terminal of the inductance 82 is coupled through a bypassing condenser 86 to the anode 85 of the discharge device 8|, while the other terminal of the inductance 82 is coupled through a condenser 83, in shunt to a resistance 89, to the control electrode 81 of the device 8|. Operating current for the discharge device 8| is supplied through a circuit which may be traced from the anode through a resistance 98, the source 29, and a portion of the inductance 82 to the cathode 84 of the device 8|.

Continuous oscillations maintained in the tuned circuit 82, 83 are transferred to an inductance 9|, coupled to the inductance 82. There is a third blade 92 of the switch 41, through'which the inductance 9| is connected in series with the resistances 39 and 58, when the switch 41 is in its downward position. The continuous oscillations produced by the oscillator comprising discharge device 8| and the tuned circuits 82, 83 are therefore effective to adjust continuously up and down the direction of radiation from the antenna I3.

The electro-n discharge device 88 is connected in shunt to the condenser 83 to simulate a condenser in a manner similar to the connection of the discharge device 26 in shunt to the condenser 25, The anode 93 of the device 88 is coupled through a condenser 94 to the ungrounded terminal of the condenser 83, and the cathode 95 of the device 88 is connected through a resistance 96 in shunt to a bypassing condenser 91 to ground, and so to the other terminal of the condenser 83. Operating current for the device 88 is supplied through a circuit, which may be traced from the anode 93 through a choke coil 98, a resistance 99, the source 29 of potential, and the resistance 93 to the cathode 95 of the discharge device 88. The screen electrode |88 is supplied with operating potential through a resistance |8| from the positive terminal of the source 29, and is bypassed to ground through a bypassing condenser |82.

A series combination of a condenser |84 and a resistance |85 is connected betweenthe anode 83 and ground to impress an alternating potential on the control electrode |83 which is leading in phase with respect to the alternating potential between the anode 93 and the cathode 95. As explained in connection with the device 26, alternating voltage between the anode 93 and cathode 95 produces a leading alternating current through the series combination of condenser |84 and resistance |85, with consequent production of a leading alternating voltage across the resistance |85, which leading voltage appears between the control electrode |83 and cathode 95. By adjustment of the average voltage across the resistance |85, the amount of leading current flowing through the discharge device 88 may be adjusted with concurrent adjustment of the frequency of the continuous oscillations maintained in the tuned circuit 82, 83.

In this connection of the transmitter, the signals from the microphone 42 are applied across the resistance |85, so that the frequency of continuous oscillations maintained in the tuned circuit 82, 83 varies in accordance with the audio signals. Consequently, the frequency at which the direction of radiation from the antenna |3 is altered up and down is varied in response to and in accordance with the signals from microphone 42. I

Wdthithe; ilares.- of the.: switch: 4:1 in? the7 above mentioned; downward-1 position; the.7 blade I-"ie connected tozground; and' the blade 46= is: coni-f nectedztlirough: az conductor' I 0; and anre'sistancev L01' to; thecontrol electrode |08.. Arnpliied-fsig-I naisl fromY the microphone l2, therefore; appeary acnossi the` resistance |05,4 change the amount or; heading current' passing' through' the; discharge devim, change the frequency of' the' continuous: oscillations maintained' in: the tuned' circuit 82,=; .changethefrequency-at whchthe amount E leadngi current passing`r through'. the device 26 is changed, and consequently change't'hefrei quency" ativehiehy the, beam of lradiationl from: the antenna'. t3 is: swept: upf and-i down in' aLv verticall plane inzresponsef tn. the intensity' of. ther signals iiroznzthe-microphone:Irl*iv litispreerredEtna-ty therate at whichfthe beam: is swept: upc. and in the: absence: of aisienslibezhighen thanv the higiiest frequency ofthe' 1 which'. it is; desiredf to transmit.4 For' ex*- ample, if'itb'edeslred toltransmit audio: sig-1 nal havingi'frequencies extending; for example, tolflOgOU cycles, itis preferredthati tliev discharge device 8| produce oscillations having a frequency higherl than'. 10,000` cycles, for exampleg. of the order ofZwGUUJ-towl cycles.

ordinary 'receiver'V designedtot detect Waves modulated in aceorda-ncewitli signals: oflessithan' 10,000 cycles, cannet respcnd'tosucha transmittedwavef. Asexplained'before, the ampliandf frequency of a transmitted'wave are constant at a-ll times; the direction of transmission-Being varied-i` A distant-receiver of theorie dinarytype receives thecarrier wave intermit tently; as" explained-in` connection with Fig.' 2; butl at suctiahighrateeof speed'as-tcv be inaudi-f ble.' An ordnary'-receiver, therefore; receives -the transmitedwave as acontinuously'V radiated;T car'd riervvcwey with no modulation;

IirFi'g 3. there'is illustrated4 a special 'receiver vvhieirl have" provicledforl reception of the AWave transmitted by the transmitter illustratedV` in'Fg.` 1 when the switch H: is in its downward .position. An antenna |10" is arrangedfto' receive the Acarrier lwave as itfpasses' the' receiver; and-to impressfit upon a receiver I'H, which comprises a: suitable;tuning,-v and amplifying apparatus-for thecarrir'wave. 'I'h'emutputfoi thereceiver isisup'piied throughs; transformer ||2- tunedby a condenser H13L tothe frequency of the carrier wave, ,upon a diode detector" Ilvr in series with la load resistance'. H55 A'high fequenc-yhy-paissing condenser IIS is connected ishunt to theoai resistance |15; `1

When the beam'is radiated from thetrans mltter irr'sucl a 'direction' as' to produce `maximum energy atV the receiver, a voltage# is produced acrossthe resistance"- 15in accordance With/the maximum intensity of: the;l carrier wave at the receiver: When the-'beam-isradiated from the transmitte'rinotheri directions4 suchitliat mini# mumv energy is received i atV the receiver, a mini'- mumvolta'geappears across' the resistance H5. The voltage across "the resistance' I t5', therefore, corresponds to the *outputy voltage A of; the tuned circuit 82"-, 89. The frequency off'tl're'u voltage across the resistanceD IIiiis; therefore; constant inl the-absence of a signalfromthe microphone 421 andvariesain` frequency from this@ constant frequency whena signal isf transmitted from the microphone Hi' The voltage@across-tlie-resistance- H55 therefore; has thecharacterls'tisofa frequency-modulated carrier wave; excepti that the average frequency may be lower thanbr'eidl frequencies. f average frechen@ is? approach mately the predetermined frequencyu at which thez tunect circuit4 |32, B operates in? the absence; or a signal' fromP themicrophone #tand as explained abbvernmy'be offV the orderofffrorni20'to 50-kilo cycles;I

A diode rectiiiercordetecter, l-lfl, and' a source H* of; potential, connectedinseriesare inshunt tof 'eine'resistancev H5;I andact as a" limiter. The potentiabot thesourceflfli isfsmadLand isusually ofT theorder of 1Y volt` The source laleis so poledv with-respect to the diode 1f as: tomaintain the dioiief non-conductive inthe absence` oi voltageresistanceV |I|5r W-hen=- the alternating voltage: across" resistance |5- has a peakvalue greater? than; the voltage 015l source |-'|:8, current news ini-the diode V||`| during suchV times and.I reducesfsuch voltagesi The function ofc-the; diode H1: and source 8l is similar' to v'the function-ora limiter` in efr-frequency: modulation receiver. SuiTcient amplification is providedini the receiver H12' so-that-signalsy are normaily* amplifiedr tof produce-` ae voltage across thefresi's't'anoe lli: greater than the potential of the source: Iflf; Thediode |2I'1 being'conductive at' all values: ofz voltageacress the resistance 5 greater than thepotential of the source ||'8, the signal voltage which can appear acrossA the diode HTi and thesource lll@ in series limited'lto# a constant maximum value Ar circuit ieconnected ini shunt-'to the-resistance IfiiLwhich circuit isarrangedfto respond: t0y the deviation' off. theffreqnency of the; voltage across resistancef'lf. from a predetermined frequency eri-nal` to the frequency to! which circuity B2, 83v` is amd@ Ict'1;i1fodu,c:elY a voltage whose polarity and magnitude'. correspondvh to? thef d-irection': and amount of such; deviation.. This voltage representgfthelsignalsnirom. the`microplione121 or the frequency of the'l continuous oscillations' mainta'inedinthe-v tuiieia circuit 3:2;v 8,3- whenf there is nozsignab themicrophone 42';

This circuiti whiclsiis' connected' in' to `the r-esistarnt:e |f|f5 com-praises` af pair of diode` rectiers |22; and"v |23;1toeachi ofi which two components; off. voltage: are:y applied., Oner componentfof voltagei'sapplied to eachoff thel diode rectifier-'s |22and |232 which: componentl is phase with the voltage: across the resistance: l |52 'Eheselatter" componentsfare apnlied tlnoughva coupling condenserf |2| connected between Y theicenterl ta'p of ifliand abpoint;between:resist-'-k ance; lits anzildetectoc' -IhtV Toit-he secondaryl of this transformer Hei't -e d-lode rectiers'f |212 and maf are' connected in'cpposmgf relation through abalaiced load' circuiti comprising' a-pair off se ries-1coiiriected;loadresistencias I aridi I'ZBL- A bypassing -cen'cfensexI |525 isconnectedxinf shunt `to thetvol load resistance'sl and; ai Seeland.'l lc'ypassing condenseri |21Y isi connected-1in.V shuziti tof the load. resistance; I 2.5;, These: two' Icypiaccia@r condensers have; low.' impednceite vcltagest the: frequency or: the voltage. across; thef resistance' l" I 5, bu-t. substant'aii imlfedance .et iti'e:'highest'.- frequency;r of sign-ar voltages. fiumi. thef microphone e2.. The circuiti is arranged;r so: thatithe aboveedescribed two components.. appliedzltofthe.: respective: diode rectieis |222 anni 128;. produce; equal andi oppor'- sitevoltageeaoros'stherespective tworesistances |24 andt. Arconductoxf: |33? isvconnectedibetween-ftlie centerftap of the'secoaryfof transformer' I |19 andaf-poi-nt lbetween theladl resistance1|2fand|f2 A seeondfcomponentl orvoltage xfrom-tiieresistarioefHfibappliedtoeachlofthe diedrectirs 9 |22 and |23. This second component is applied through the transformer action of the transformer I |9, whose primary isconnected in shunt to resistance and whose secondary, shunted by a condenser |22, forms a tuned circuit. If the frequency of the voltage across resistance I I5 is the same as the resonant frequency of the tuned circuit, including the condenser |20 and the transformer H9, the transformer ||9 impresses a voltage on one of the diode rectiers, which voltage leads by substantially 90 the voltage across the resistance I I5. The tuned transformer applies across the other diode rectifier a voltage of equal magnitude, which voltage lags, by substantially 90, the voltage across the resistance ||5.

As the frequency of the voltage across theresistance I I5 changes, this phase relation between the various components changes, so that the two components across one diode rectifier are more nearly in phase, and the two components across the other diode rectifier are more nearly out of phase. The resultant voltage aeross one diode, therefore, becomes greater than that across the other, when the frequency of the voltage across resistance ||5 is different from the resonant frequency of the tuned circuit including the condenser |20 and the transformer I I9. Under such conditions a greater rectified voltage appears across one of the load resistances |24 and |25 than across the other, and a net signal Voltage is therefore present across the series combination of the two load resistanzes. i

The signal voltage across the resistances |24 and |25 is transmitted through a coupling condenser |28 to the input of an audio amplifier |29, which amplifes the signal and transmits it to av loud speaker |30.

By further adjustment of the switch 41, the transmitter illustrated in Fig. 1 may be utilized for a third type of transmission in which the beam from the antenna I3 is swept up and down in a vertical plane at a constant rate, while the frequency of the carrier wave is modulated in response to the intensity of a signal. In this third connection of the transmitter, continuous variation of the direction of transmission of radiation from the antenna I3 assures reception at the distant receiver, as explained above in con. nection with Fig. 2, while modulation of the frequency of the carrier wave in response to the intensity ofan ,audio signal provides signal transmission without selective fading associated with multi-path transmission, such as occurs with an amplitude modulated wave.

Such a reconnection of the transmitter may be effected by moving the blades of the switch 41 to the upper position, in which audio signals from the microphone 42 are caused to Vary the ferquency of oscillations in the tuned circuit I0 in `response to the intensity of the signals. With this reconnection, no signal voltage is applied across the resistance |65, with the result that a constant current flows through the anode and -cathode of the electron discharge device 80, so

l0 comprises an electron discharge device |40. which is interconnected with the tuned circuit I0 in the same Way as the electron discharge device is interconnected with the tuned circuit 82, 83. The anode |4| of the device |40 is coupled through a coupling condenser |42' to the ungrounded terminal of the tuned circuit I0, and the cathode |43 is connected through a resistance |44, in shunt to a bypassing condenser |45, to ground, thereby being coupled to the grounded terminal of the tuned circuit I0. Voltage between the terminals of the tuned circuit I0 therefore appears between the anode |4| and the cathode |43, the device |40 being arranged-to transmit a leading current through its anode and cathode. I

The anode |4| of the device |40 is supplied with operating current through a choke coi1'I46 and a resistance |41 from the'positive terminal of the source 22. The screen electrode |48 of the device |40 is connected through a resistance |50 to this positive terminal, and is bypassed to ground through a bypassing condenser |49.

A suitable phase shifting network applies an alternating potential to the control electrode |52 of the device |40, which potential is leading with respect to the alternating voltage between the anode |4I and the cathode |43. This network comprises a series combination of a condenser |5| and a resistance |53 connected in shunt to the tuned circuit |0. The control electrode |52 is connected to a point between the condenser |5| and the resistance |53. Alternating voltage between the terminals of the tuned circuit I0 appears across the series combination of condenser |5| and resistance |53, and produces a leading current flowing therethrough. This leading current produces a leading voltage across the resistance |53, which leading voltage appears between the control electrode |52 and the cathode |43. The leading voltage on the control electrode |52 in turn allows a current to flow between the anode |4| and the cathode |43, which current is leading with respect to the voltage across the terminals of the tuned circuit |0.

Since the discharge device |40 transmits leading current between its anode I4| and cathode |43 it simulates a condenser connected in shunt to the turned circuit I0, so that the tuned circuit resonates at a lower frequency. Adjustment of the average voltage across the resistance |53 determines the amount of alternating current flowing through the device |40, and in turn determines the apparent size of the condenser which is simulated, so that the resonant frequency of the tuned circuit I0 is thereby adjusted.

In the upward position of the switch 41, signals from the microphone 42, amplified through the amplifier 43 and transmitted through the transformer 44, are impressed, through the switch blades 45 and46, between ground and a conductor |54, which is connected to the control electrode |52. The amount of leading alternating current flowing through the anode |4| and cathode |43 of the device |40 is therefore adjusted in response to the intensity of signals from the microphone 42, whereby the frequency of oscillations from the tuned circuit I0, and consequently the frequency of radiation from the antenna I3, is adjusted in response to the intensity of such signals.` f

As mentionedpreviously, the transmitter, when so connected, cyclically varies the direction-of radiation from the antenna I3 up and down in a vertical plane at a constant frequency, and varies the frequency of such radiation in response to ill theiintensity ci signals from the microphone I2.

It .is a common characteristic .of all forms o! my :invention that the intensity of 'the radiated carrier wave =is preferably vmaintained constant, While 'signals are transmitted "by 'variation or Va .directional characteristic of the radiation, such of the direction Yof propagation of ta vtix-variation of `the axis of -polarization of "the B y maintaining the carrier Vwave -intensity constant, it is assured that a maximum amount of -radiation iis `received at the receiver at all times. The vagaries of reiiection from :the 11.1'Jper Strata of the atmosphere -produce a `minimum correspondence between variations of the .reflection coeicient andvariationofithe intensity DI the radiation 'with resulting distortion of -sig- ;na'l, when such signals are tra-nsmitted fby variation 'ci' .a directional characteristic yof the lwave .rather than 'variation of iits intensity. The ilimiter device illustrated *in Fig. '3 is useful i-n aid- Jlng "in `the reduction of variation o1 Aintensity of received signals due to such -vaziyfing lreflection from the'upper atmosphere.

In Fig. 4, there 'is illustrated -a 'radio 4transitriitterwhic'h alters the axis of polarization lof radia- JVtion between vertical and horizontal '-planes re sponse to a function for the intensity of la signal. Intisgurafa carrierwvave generator flll transmils oscillations *th-rough ltwo electron discharge devices Y|61 'and N2, respectively 'fto a pai-rief an- *termae t5! and 1N. The :antenna xr|81 'is ar- .ranged to radiate vertically vpolarizsed 'radio Waves, While the antenna |64 Eis arranged Ito radiate thorizontally `-xgioilarized Waves. Suitable means .lncluding an audio amplifier 155 gis provided to make `the electron discharge devices l-fifl and :162 alternately conductive -inresponse to the intensity of signals from -amicrophone im.

oscillations from thecarrier wave generator 160 are transmitted through a tuned transformer 'H5-l to the control circuit .of vthe vdiselfiarge device 46|, which circuit may be traced from fthe control electrode T68 through lthe'tuned secondary'oi fthe transformer Til., a resistance 169 in shunt "to a bypassing condenser "ITD, and-asource Ill I of bias `.potential "to the cathode `|12 -of the device Bil. The output circuit of the device Mill may -lbe traced from the anode 'l1-3 through a tuned transformer 1.14 which is ycoupled to the antenna N3, and a Vsource 115 of operating potential -to the .cathode |12.

.Qscillations from the carrier wave generator .lill are similarly transferred to Jthe input circuit of the discharge device H2 through a tuned transiormer H6. 'The input 'circuit vof vthe -dey vice I B2 'may ;.be"traced from the Ycontrol electrode H1 through the secondary of the ftuned transformer 116 aresistance l in Yshunt Ato a '.cy- Vpassing condenser T19, 4and 'the source 41111 of potential to the cathode "|80 of the device 1102. The output circuit of vthe device 452 ,may :be Jtraced anode |81 through a tuned trans- Iormer .1'82 'which `is -coupled'to lthe vantenna 134, the source T75 ol potential to the cathode 'fingly positive potential across one yor the resistances i169 and 118, while 'impressing an iincreasingly vnegati-vepotential `across the other kof the '-res'istances. Such potentials, increasing Ain Aopposite polarity, make one Yof the `electron discharge devices 1I-'-I :and |62 more conductive, `While making 'the other device less conductive. Consequently, oscillations from the generator 'I 6U 'are "transferred Vto the antennae '|263 vand :itl .in 4relative amounts .which rare varied in response to ythe intensity of signals Ifrom the microphone 1566.

:Any receiver suitable :for receiving vamplitude modulated 4.waves l.may .be used with `the transmitter Vof Fig. 4 if .the accompanying receiving antenna is more effective to receive Waves of one Vpolarization than of another. Such 'an antenna 7may l'conveniently vbe fformed, for example, by -a straight conductor.

`It is'to be understood that Ait Vis withinthe scope of =my :invention Ato utilize modulation of .more

than one .directional characteristic of the zradi- .ated yWave, fas, vfor example, -it'o utilize modulation of Aa beam 1in lboth vertical .and horizontal l.planes concurrently vwith modulation of rthe faxis .of polarization yof the ibeam. Also, the amplitude .or frequency yof 'thefcarrler LWave,.if desired, "may be modulated concurrently lwith .modulation of ang,I :directional characteristic ofthe radiated wave, although it is preferred to maintain the :ampli- 'tude .of Lthe Wave constant. The transmitter of Rig. 4 may also be :modified :similarly to that of Fig. 1, so that the frequency of modulation vof the plane :of polarization `of the wave is varied in response tothe intensity of a signal, or alternatively lat .a :constant lfrequency, while the carrier .frequency is modulated in response `to vthe signal. The receiver of Fig. 3 with a .straight wire .antenna is suitable .for receiving lsuch Vva fsignal in 4which the frequency vof .variation of the plane .of tpolarization :is Jvariedrin:acccndance with the ,in- .ftensity of .the zsignal.

While I have .shown and Ydescribed particular of my invention. eitfwill be y,obvious to :those skilledin the art that changes and modications may be made without departing from my 3inventionginits broader aspects, and I, therefore,.aim in the Vappendedfclaims to cover all such changes `and:modifications as fall within fthe true spirit and scope of my invention.

iWfhat .I nclaim :as new and :desire to secure Iby Letters Patent of the United .States i1. In combination, :a radio transmitter, .a radio receiver, said transmitter and receiver Abeing so spaced that waves from said transmitter arrive at vsaid receiver principally by reason -of reflection from the higher .strata lof the atmosphera'means 4to radiate from :said transmitter a wave of constantintensi'ty and to .modulate the direction of propagation of said wave at fa frequency modu- :lated in ,response to a :desired signal, said :fre- :quenc'y being substantially .higher-than the highest vfrequency .of said signal, whereby said vWave :appears at theflocation of said receiver witlrmodulations of `intensity in accordance with fa funcltion ofsaiddesired signal, means in said receiver responsive :to said modulations of intensity for producing a wave whose frequency corresponds -to the *frequency at wlhichthe direction of .propagation of said wave is modulated, and means responsive to frequency variations of .said Ilast means for reproducing said signal.

f2. In combination, .a radio transmitter, a radio said receiver being so spaced :from said tranmntter that Waves from :said transmitter ar rive at said receiver principally by reason of rcflection from the higher strata of the atmosphere, means to radiate from said transmitter a wave of constant intensity and to modulate the plane of polarization of said wave at a frequency modulated in response to a desired signal, said frequency being substantially higher than' the highest frequency of said signal, means for causing said receiver to receive said wave in greater intensity when polarized in one plane than when polarized in another plane, whereby said receiver receives said Wave with modulations in intensity in accordance with a function of said signal and variations of reflection from said higher strata affect the received intensity in minimum amount, and means in said receiver responsive to said modulations in intensity for reproducing said signal.

3. In combination, a radio transmitter, a radio receiver, said receiver being spaced from said transmitter by sufficient distance that the path of transmission of waves between said transmitter and receiver may be adversely affected by disturbances to which said path is subject, means to radiate from said transmitter a Wave having its plane of polarization modulated at a frequency modulated'in response to a desired signal, said frequency being substantially higher than the highest frequency of said signal, means for causing said receiver to respond predominantly to said wave when polarized in a particular plane, whereby amplitude modulations of said Wave caused by said disturbances produce minimum effect on said receiver and said receiver receives said wave with modulations of intensity in accordance with a function of said signal, and means in said receiver responsive to said modulations of intensity forreproducing said signal.

4. In a signal transmission system, a signal source, means for radiating a carrier wave, means for modulating the axis of polarization of said carrier wave at a frequency modulated in accordance with the intensity of said signal, and means responsive to modulations of the axis of polarization of said Wave to receive said Wave and reproduce said signal.

5. In a signal transmission system, a signal source, means for radiating a carrier wave, means for cyclically varying a directional characteristic of said Wave at a predetermined frequency, means responsive to the intensity of a signal from said source for varying the frequency of cyclic variation of said characteristic, and means responsive to variation of the frequency of cyclic variation of the directional characteristic of said Wave to receive said wave and reproduce said signal.

6. In a signal transmission system, a radio receiver comprising means to receive a carrier Wave at different intensities as a cyclically varying directional characteristic thereof varies, the frequency of variation of said characteristic varying from a predetermined frequency in accordance with the intensity of a signal, means for detecting said received carrier wave to produce a. voltage of which the intensity varies at a frequency corresponding to the frequency at which said directional characteristic varies, and means responsive to variations of the frequency of said voltage from said predetermined frequency to reproduce said signal,

7. In a signal transmission system, a radio receiver arranged to respond to a beam of radio waves sweeping past said receiver periodically, whereby said waves are received by said receiver with modulations of intensity, the frequency of 'sweep of said waves past said receiver varying from a predetermined frequency in accordance with the intensity of a signal, means in said receiver for detecting said waves to produce a voltage of which the intensity varies at a frequency corresponding to the frequency of sweep of said Waves, and means responsive to variation of the frequency of said voltage from said predetermined frequency to reproduce said signal.

8. In a signal transmission system, a radio receiver arranged to respond to polarized radio waves impinging on said receiver with a varying axis of polarization, the frequency of variation of said axis varying from a predetermined frequency in accordance with the intensity of a signal, means responsive to variation of the axis of polarization of said waves for receiving said waves at different intensities as said axis of polarization varies, means in said receiver for detecting said received Waves to produce a voltage of which the intensity varies at a frequency corresponding to the frequency at which said axis varies, and means responsive to variation of the frequency of said voltage from said predetermined frequency to reproduce said signal.

9. In a signal transmission system, a signal source, means for radiating a carrier Wave of a predetermined frequency, means for varying a directional characteristic of said radiated carrier wave cyclically at a predetermined frequency, means responsive to the intensity of a signal from said source for modulating the frequency of cyclic variation of said directional characteristic, a receiver located at a position with respect to said radiating means where said carrier wave'affects said receiver, means in said receiver for producing a Wave Whose frequency corresponds to the frequency of said cyclic variation, and means responsive to frequency variations of said last Wave for reproducing said signal.

10. In a signal transmission system, a radio transmitter comprising a carrier wave source, a signal source, an antenna energized from said carrier Wave source and arranged to radiate a carrier wave from said source, means for reflecting the radiated carrier wave in different directions, and means for adjusting said reflecting means to alter the direction of reflection of said carrier wave cyclically at a frequency modulated in accordance with a function of the intensity of a signal from said signal source.

11. In combination, a radiator, a reflector arranged to adjust the direction of propagation of Waves radiated by said radiator in accordance with the tuning thereof, means responsive to Waves received by said reflector from said radiator for adjusting said tuning, a signal source, and means to adjust said last means to vary said tuning in response to signals from said source.

l2. In combination, a half wave dipole radiator, a dipole reflector arranged parallel to said radiator to adjust the direction of propagation of waves radiated from said radiator in accordance With the tuning thereof, means comprising a series resonant circuitl connected between separated halves of said reflector to adjust the tuning thereof, and means to adjust the resonant frequency of said resonant circuit with respect to the frequency of said Waves to vary the tuning of said reflector in response to signals to be transmitted.

13. In a signal transmission system, a signal source, a first Wave source, means for radiating a second Wave, means for modulating the plane of polarization of said second wave cyclically in response to the intensity of the Wave from said i rst :wave fsource, `and means responsive to fa. function V,of .sthe 'intensity sof :a :signal rom saidv signal source for modulating,theffrequencyiof-one of said waves.

M. :In 1a signal transmission fsystem, La. -sgnal .sourcemeans forradating-a`carrerwave means for c yclically varying the :plane 1 of polarization 'of said Wave fat a. `predetelmined frequency, ,and meansresponsiveiozthe intensity ofea signal from said source l,for varying fthe frequency Lof cyclic variation ,of :'said plane of polarization.

EHALSELY W.

,REFERENCES :CITED The illowing rferences are of recordln the "15 le of Lthis Apatent:

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